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UBC Theses and Dissertations

Determination of microparameters for discrete element modelling of granular materials with varying particle size using one-dimensional compression testing Mei, Chen-Jung Judy


A research program was undertaken to study the effect of particle size on the mechanical response of granular materials, with particular emphasis on supporting the study of the effect of backfill particle size on the soil-pipe interaction of buried pipelines. In this regard, laboratory one-dimensional compression tests of different-sized glass beads and crushed granite were conducted. One-dimensional compression tests on glass beads were simulated in a numerically equivalent discrete element model (DEM), in order to identify suitable DEM particle stiffness microparameters able to reproduce the corresponding laboratory results. Effects of particle size on bulk material behavior were first studied through the analysis of experimental one-dimensional compression test results of both glass beads and crushed granite. Axial stress-strain response of both materials revealed that an increase in particle size of a granular material matrix increased the stiffness of the overall granular matrix. Results also revealed that smaller particles resulted in higher side wall friction values than larger particles of the same material type. The dependence of constrained modulus and shear modulus on effective confining stress determined experimentally from all laboratory tests were in general agreement with relationships previously proposed by other researchers. Numerical simulations of the laboratory specimens were conducted using DEM; i.e. the numerical models were calibrated against experimental results obtained from one-dimensional compression tests of different-sized glass beads to determine suitable particle stiffness microparameters for granular materials of differing particle sizes. The findings indicated that the numerical value of particle stiffness microparameters increased with increasing particle size. In agreement with the experimental results, DEM results also showed that an increase in particle size resulted in increased stiffness of the overall granular matrix under one-dimensional compression. Through evaluation of numerical results, it was proposed that a preliminary relationship between “average” constrained modulus and particle stiffness could be established. Results indicate that DEM simulations of one-dimensional compression tests can be successfully used to calibrate DEM particle stiffness microparameters. The findings suggest that particle stiffness microparameters should be carefully selected for DEM simulations of granular materials of different-sized particles and, in turn, be utilized in quantitative analysis of geotechnical engineering problems.

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